The present invention relates, broadly, to the field of atomization of liquids for dispersal in the form of aerosols. More specifically, the invention relates to means for the distribution of a liquid active material, such as a perfume, air freshener, insecticide formulation, or other material, in the form of fine particles or droplets, as in a fine spray, by means of a piezoelectric device. In particular, the invention is directed to a piezoelectric liquid delivery system for the production of droplets of liquid, or liquid suspensions, by means of an electomechanical or electroacoustical actuator. More specifically, the present invention relates to a battery operated piezoelectric dispenser utilizing an orifice plate in communication with a piezoelectric element. It has been found that by joining the orifice plate to the vibrating piezoelectric element by a soldering method, rather than the conventional adhesive or bonding techniques, performance degradation of the piezoelectric atomization, i.e. a decline in release rate, is avoided. This is of particular value in the atomization of perfumes and fragrance oils, which attack the normal adhesives, especially under high rates of flexing or vibration.
The distribution of liquids by formation of a fine spray, or atomization, is well known. One method for such distribution is to atomize a liquid by means of the acoustic vibration generated by an ultrasonic piezoelectric vibrator. An example of such a method is shown in Carter, U.S. Pat. No. 4,702,418, which discloses an aerosol dispenser including a nozzle chamber for holding fluid to be dispensed, and a diaphragm forming at least a portion of the chamber. An aerosol dispensing nozzle is disposed therein, with a restrictive passage for introducing fluid from the reservoir to the nozzle. A pulse generator in combination with a low voltage power source is used to drive a piezoelectric bender, which drives fluid from the reservoir through the nozzle to create an aerosol spray.
Another atomizer spraying device is shown by Humberstone et al, in U.S. Pat. No. 5,518,179, which teaches a fluid droplet production apparatus comprising a membrane which is vibrated by an actuator which has a composite thin-walled structure, and is arranged to operate in a bending mode. Fluid is supplied directly to a surface of the membrane and sprayed therefrom in fine droplets upon vibration of the membrane.
U.S. Pat. No. 5,297,734 of Toda teaches ultrasonic atomizing devices comprising piezoelectric vibrators with a vibrating plate connected thereto, by means of a conductive adhesive. In this patent, the vibrating plate is described as having a large number of minute holes therein for passage of the fluid.
Ivri et al, in U.S. Pat. No. 5,586,550, teach apparatus for the delivery of therapeutic liquids, including a vibratable non-planar member having tapered apertures, to which liquid is delivered by squeezing a liquid reservoir to deposit it directly on the surface, in such a manner that all of the liquid adheres to the vibratable member by surface tension. The piezoelectric element is bonded to a vibratory cantilever beam to provide oscillation to a carrier plate and thin shell non-planar member so as to nebulize the liquid in contact therewith.
U.S. Pat. No. 4,479,609, of Maeda et al, discloses a liquid sprayer comprising an ultrasonic vibrator, a liquid supply chamber, and a liquid absorber for transporting liquid from the chamber to the vibrator. The electrostrictive element is connected to the metallic horn by a conductive adhesive. Further, in U.S. Pat. No. 4,533,082, Machara et al teach an arrangement for discharging liquid droplets, wherein a piezoelectric transducer is secured to a vibrating member to induce a displacement of the liquid through a nozzle opening. An axially vibrating disc is cemented to a ring shaped piezoelectric transducer of polarized ceramic. The disclosures of these patents, and of all other publications referred to herein, are incorporated by reference as if fully set forth herein.
Such atomizers and/or dispensers fail to provide a system by which liquid to be dispersed is supplied to the vibratory mechanism/surface without resulting in corrosion, solvent activity by the active liquid, or bond failure at the point of joining of the piezoelectric element and the orifice plate, particularly when the active liquids are such as perfumes or insecticides, having high activity quotients at high rates of vibration. Moreover, the prior art has failed to provide an easily portable, battery operated, continuous-action dispenser employing an orifice plate in soldered connection with a ceramic piezoelectric element, capable of long periods of use with little or no variation in the delivery rate. Thus, a need exists for an improved method for joining piezoelectric transducers to orifice plates or other elements of a piezoelectric atomizer.
It is an object of the present invention to provide a highly efficient, consistent, and reliable dispenser for liquid active materials, employing an orifice plate securely joined with a ceramic piezoelectric element. While the invention is described as comprising a ceramic piezoelectric element, it is understood that the invention is not limited thereto, but also extends to other piezoelectric materials having the requisite properties for use, and resistance to the elevated temperatures which accompany joining elements by soldering. By liquid active materials, it is meant to include such liquids as perfumes, air fresheners, household cleaning materials, disinfectants, repellants, insecticides, aroma therapy formulations, medicinals, therapeutic liquids, or other liquids or liquid suspensions which benefit from atomization for use. These compositions may be aqueous, or comprise various solvents. In a preferred embodiment of the invention, the piezoelectric liquid delivery system is easily portable, battery operated, and conveniently refillable with the same, or a different, liquid active
It is a further object to provide a piezoelectric pump capable of operating efficiently for months, on low voltage batteries, while maintaining consistency of delivery throughout the period. Included in such object is to provide a piezoelectric atomizer suitable for use with such electrical sources as 9 volt batteries, conventional dry cells such as xe2x80x9cAxe2x80x9d, xe2x80x9cAAxe2x80x9d, xe2x80x9cAAAxe2x80x9d, xe2x80x9cCxe2x80x9d, and xe2x80x9cDxe2x80x9d cells, button cells, watch batteries, and solar cells or solar power. The preferred energy sources for utilization in combination with the present invention are xe2x80x9cAAxe2x80x9d and xe2x80x9cAAAxe2x80x9d cells.
In still another object, it is desired to provide a liquid delivery system capable of atomizing fragrance oil or insecticide formulation linearly over time, while maintaining the same character/composition on the last day as was delivered on the first, i.e. with no component change or separation with time. The electronics of such a unit may preferably be programmable, and may be used to set a precise delivery rate (e.g. in milligrams per hour, or mg/hr), or may allow the consumer to adjust intensity or effectiveness to a desired level for personal preference, efficacy, or for room size.
Another object of this invention is to provide small droplets of pure fragrance or insecticide formulation which are propelled intermittently from the unit to form a small xe2x80x9ccloudxe2x80x9d or xe2x80x9cpuff,xe2x80x9d which droplets quickly diffuse and move throughout a large area on air currents present in said area. It is found that the small size of such droplets, and the correspondingly large ratio of surface area to mass, result in these droplets evaporating quickly and uniformly. In preferred embodiments, the delivery system operates with a linear delivery rate for several months on a single 1.5 volt xe2x80x9cAAxe2x80x9d size battery, delivering uniform volumes of essentially equally sized droplets of the liquid for the entire period.
These and other objects of this invention are achieved by a piezoelectric dispenser for fragrances, insecticide formulations, and other highly active liquids, wherein the dispenser includes a chamber for the liquid to be dispensed, means to supply the liquid from said chamber to an orifice plate for dispersal of the liquid, and a ceramic piezoelectric element, wherein the piezoelectric element is joined to the orifice plate by soldering, to achieve a bond which is superior to conventional adhesive bonding.
The fragrance or insecticide formulation is supplied to the back side of the orifice plate through a capillary feed system that delivers the liquid in surface tension contact with the plate, without damping the vibrational frequency to which the plate is subjected by the piezoelectric element. The piezoelectric element is driven by a small battery, capable of exciting the element and causing it to force liquid through the orifice plate, which has a multitude of small tapered or conical holes therein perpendicular to the surfaces thereof, the exit of said holes being on the order of 6 microns in diameter. Timing circuitry is used to provide an intermittent excitation to the piezoelectric element so as to dispense small droplets of said liquid in a time dependent fashion. Due to the nature of the liquids being atomized, i.e. the presence of organic components or solvents in the fragrance oils and/or insecticide formulations, it was found that conventional bonding methods for joining the orifice plate to the metallic cantilever beam of a conventional piezoelectric driver were inadequate. Conventional bonding agent exhibit significant degradation over time when in contact with fragrance oils, with the degradation believed to be accelerated by the flexing forces caused by the piezoelectric vibration. A soldering process was developed to eliminate this problem, using a lead/tin solder. In addition, it was found that the orifice plate could be attached directly to a piezoelectric ceramic element, eliminating the need for an extra part such as a cantilever beam or metal amplifying plate.
These and still other objects and advantages of the present invention will be apparent from the description which follows, which is, however, merely of the preferred embodiments. Thus, the claims should be looked to in order to understand the full scope of the invention.